This invention relates to a process for the synthesis of 1,2-benzothiazine-3-carboxamides, and in particular to the preparation of N-aryl-3,4-dihydro-2-alkyl-4-oxo-2H-1,2-benzothiazine-3-carboxamide 1,1-dioxides, a class of compounds useful as antiinflammatory agents, and to N-aryl-N'-alkyl-N'-(2'-alkoxycarbonylbenzenesulfonyl) glycineamides as useful intermediates for said process.
Synthesis of 3,4-dihydro-2-alkyl-4-oxo-2H-1,2-benzothiazine-3-carboxamide 1,1-dioxides has been previously achieved by amination of the corresponding 3-carboxylic acid ester or by treatment of the parent 3,4-dihydro-2-alkyl-4-oxo-2H-1,2-benzothiazine 1,1-dioxide with the appropriate isocyanate, Lombardino, et al., J. Med. Chem., 14, 1171 (1971) and Zinnes, et al., ibid., 16, 43 (1973) and U.S. Pat. No. 3,591,584. In addition, Zinnes, et. al., loc. cit., has taught the preparation of 3-carboxamides by treatment of the pyrrolidine enamine of 3,4-dihydro-2-methyl-4-oxo-2H-1,2-benzothiazine 1,1-dioxide with phosgene followed by treatment of the resulting 3-carbonyl chloride with an appropriate amine.
U.S. Pat. No. 3,714,155 discloses 4-hydroxy-2,N-dimethyl-2H-1,2-benzothiazine-3-carboxanilide 1,1-dioxides as antiinflammatory agents, synthesized by methylation of the corresponding N-phenyl carboxamide with dimethylsulfate in the presence of sodium hydride.